The invention relates to a lance for processing molten metal baths located in metallurgical tanks, particularly steel subjected to a vacuum in RH tanks and furthermore for heating the RH tanks prior to or between processing phases, and having an internal guide pipe for conducting gases, in particular oxygen, with a lance mouth located at its head end for blowing the gas and with a first cooling jacket over its entire length and that is connected at its foot end to gas and cooling media supplies, whereby for executing a burner function the lance has channels arranged on the exterior circumference of the first cooling jacket for the purpose of feeding a fuel gas to burner nozzles formed in the region of the head-end lance mouth and oriented at an oblique angle to the longitudinal axis and the fuel gas channels are enclosed by a second external cooling jacket.
DE 44 42 362 C1 describes a lance for processing molten metal baths that has the aforesaid features. The multifunction lance known herefrom permits blowing oxygen with and without solids and permits a burner flame to be generated for heating the tank, steps that are independent of each other. When oxygen is blown, the oxygen is blown via the internal guide pipe provided with a Laval-type lance mouth, while when in the burner mode the fuel gas channels admit fuel gas so that in the region of the lance mouth the desired flame is formed when a combustion reaction takes place as the oxygen discharges in the burner mode.
The known multifunction lance is associated with the disadvantage that during the oxygen blowing process and during the subsequent deep-vacuum processing, due to the somewhat strong reaction of the molten metal bath to be processed, slag and/or metal can spatter so that the burner nozzles at the end of the multifunction lance are affected and are thus no longer available for subsequent burner operations. Known in order to avoid this is keeping the burner nozzles clear by means of an inert gas inserted into the fuel gas channels during the entire process; this is correspondingly expensive.
The object of the invention is therefore to provide a lance with the features cited in the foregoing in which there is both an oxygen blowing mode and a burner mode, said modes being independent of each other, and in which the burner nozzles are protected against becoming plugged up by spattered material without the burner nozzles having to be supplied with inert gas.
This object is achieved, including advantageous embodiments and further developments of the invention, from the contents of the patent claims that follow this specification.
The basic idea behind the invention provides that the internal guide pipe with the first cooling jacket is embodied as a first lance body and the fuel gas channels with the second cooling jacket are embodied as a second lance body and the first lance body is displaceably arranged in the second lance body and can be shifted between a raised position in which it operates as a burner and a lowered position in which it operates as a blower and in which the burner nozzles are covered by the first lance body, which projects downward in relation to the end of the second lance body.
The invention is associated with the advantage that the lance can be shifted from the oxygen-blowing function to the burner function by simply displacing the first lance body in the second lance body, whereby in the oxygen-blowing mode the first lance body overlays the second lance body that has the burner nozzles such that the first lance body completely covers the burner nozzles, which are oriented at an oblique angle to its longitudinal axis, and mechanically protects the burner nozzles from spattered material. This provides the burner nozzles with protection that is effective and easy to use. An additional advantage is that the existing lance, which previously was configured solely as an oxygen blower, is reconfigured by means of a second lance body placed thereover and thus can be provided as a combined lance for operating as both blower and burner.
In accordance with one exemplary embodiment of the invention it is provided that the second lance body annularly encloses the first lance body so that the lance can be operated concentric to the RH tank axis in both burner and blower modes.
Furthermore provided in accordance with one exemplary embodiment of the invention is that the first lance body can be displaced in the second lance body for infinitely variable spacing of the burner nozzles from the burner mouth of the second lance body. This is associated with the particular advantage that it is possible to obtain optimum combustion of the fuel gas introduced due to the variably adjustable spacing of the burner nozzles relative to the lance mouth for the oxygen outlet. In burner mode as a rule only about ⅕ to {fraction (1/10)} of the quantity of oxygen has to be fed through the internal guide pipe of the lance compared to the quantity of oxygen used during blowing operations, so the Laval nozzle formed in the region of the lance mouth does not work and the discharge conditions for the oxygen are completely different here compared to the conditions in the oxygen-blowing mode. This can be accomplished by optimally adjusting the spacing of the burner nozzles relative to the lance mouth while paying attention to the stoichiometric relationship of oxygen to fuel gas. Since a substantial amount of water is associated with the reaction of the fuel gas with the oxygen, optimizing the spacing of the burner nozzles from the site at which the oxygen discharges can reduce the amount of water that necessarily occurs during the heating process.
With regard to the lift attachment of the first lance body and its displaceability in the second lance body, it can be provided that the first lance body can be moved by a lift apparatus that is attached to the second lance body. In this embodiment the second lance body can be embodied correspondingly shorter.
Alternatively, it can be provided that the second lance body extends over the entire length of the first lance body and that separately arranged lift apparatus are provided for the first lance body and for the second lance body. In this case both lance bodies are guided through the packing gland arranged in the cover of the processing tank so that the appropriate lift apparatus then assume the spacing function for the two lance bodies when in the burner mode.